A Tory, Bill Wiggin, started by saying that we had one of the largest budget deficits of any first world economy. "Does the prime minister regret that?"

"No," said Gordon Brown, to happy chortles from those who do not wish him well, many of them Conservatives.

It was a "have you stopped beating your wife?" question, unanswerable on its own terms. What he wanted to say was: "No, because we actually have the second lowest debt of any G7 country."

This is pure creative accounting, like saying you are not personally in debt, apart from your £200,000 mortgage, which doesn't count.

David Cameron asked two questions about preparations for the freezing weather. Mr Brown answered at interminable length. I was reminded of Nye Bevan who said, approximately: "This island is made largely of salt and surrounded by sand. Only an organising genius could produce a shortage of salt and grit at the same time."

The prime minister announced that there were now depots where salt could be obtained. These are known as "salt cells". Like "pepper grinds" or "ketchup botts". People laughed, disbelievingly. Things were getting surreal.

Mr Brown attacked the new Tory poster with the smoothie-chops picture of David Cameron. Admittedly it looks as if someone had tried to play Mr Potato Head with a piece of veal. But it is recognisably the Tory leader. "You look very different from the poster we see," said Brown, adding that the Tories had posters but Labour had policies.

Mr Cameron next pulled a stunt which nobody should have fallen for. "When it comes to Labour members' election addresses, who is going to put the prime minister's picture on the front?"

This is a heffalump trap, clearly marked with a flashing neon sign saying "heffalump trap". Four Labour members, all with less common sense than Winnie the Pooh, stepped in and raised their hands. Huge mistake.

Mr Cameron gloated. "Six of them do not want him in the cabinet, and just four are going to put his picture on their election addresses! He is being airbrushed out of the campaign!"

Mr Brown reached into his own bag of tricks and reminded Mr Cameron that he had changed his policy on marriage allowances three times. "You need three TV election debates because you have three versions of the same policy!"

So Cameron quoted Douglas Alexander, the international development secretary, who may or may not have something to do with the Labour campaign, this week at least. He had said that Labour itself has no policies. "For God's sake, Harriet's helping to write the manifesto!"

Ms Harman gave what looked like a girly smile. Imagine being surrounded by bitter rivals and enemies, nearly all on your own side, and the only response you're allowed is a girly smile.

The Conservative leader wound up by saying that the Cabinet and Labour party were "too disloyal to support the prime minister, but too incompetent to remove him".

The last, feeblest, wettest reply of the lot came from, I fear, Gordon Brown: "I must say that your airburshed poster had better lines on it than the lines you are delivering."